I'm interesting in converting the Hex code which is produced when I compile a program into assembly, I've heared that you need some kind of disassembly for the exact microcontroller that is being programmed. in my arduino i have atmega168. anyone knows where i can find a disassembly program for this chip?

The hex file contains the runtime machine code, it's what Arduino will get when you upload a sketch. But the hex file has all of the high level information stripped out so even if you had a dissassembler you would find the output much more difficult to interpret than the output from avr-objdump.